The identification and selection of an antibacterial chemotherapeutic agent for development depends on several properties. These include in vitro potency against bacteria, in vivo efficacy in animals and man, pharmacokinetic parameters such as good plasma levels and favorable metabolism, and reduced side effects and toxicity. The ideal agent should have the best blend of these properties.
Within the quinolone/naphthyridone class of antibacterials, efforts are directed toward increasing in vitro and in vivo efficacy while lowering certain side effects such as phototoxicity and cytotoxicity and reducing general toxicity as well.
It is also known that within the chiral environment of living organisms, individual stereoisomers/enantiomers of drugs may show unique properties relative to the racemic mixtures. When this occurs, the optimal properties of the drug can only be obtained when the most favorable stereoisomer is utilized in its pure chiral form.
U.S. Pat. No. 4,665,079 shows quinolones and naphthyridines by structural formula to have 7-[3-(1-amino-1-alkylmethyl)-1-pyrrolidinyl] side chains. These compounds of formula A, where R.sub.1 or R.sub.2 ##STR1## are alkyl or hydrogen were revealed to have good in vitro antibacterial potency. European Patent Publication 207,420 describes quinolones/naphthyridones substituted at C.sub.7 with such compounds as A having the two asymmetric centers, and the preparation of two diastereomeric mixtures, each containing two nonseparable enantiomers. These mixtures are now known to consist of the formulas of mixture B and mixture C. ##STR2## The mixtures B and C (of unknown composition) were described to possess improved in vivo activity relative to unsubstituted compounds (those of formula A where R.sub.1 and R.sub.2 are both hydrogen). All data reported were for the mixtures, and no method of separation of the mixtures was described. At the International Congress of Antimicrobial Agents and Chemotherapy (ICAAC) in Houston, Tex., 1989, there were reported certain individual enantiomers of 1-ethyl and 1-cyclopropyl-6,8-difluoroquinolone-3-carboxylic acids. The 3-(R)-1' (S) enantiomers were disclosed to have the most potent activity in vitro. One stereoisomer (3R, 1'S) was shown to have improved in vivo efficacy relative to an unsubstituted compound (formula A where R.sub.1 and R.sub.2 are both hydrogen). Except for the in vitro data, no other comparisons among the pure stereoisomers were provided.
It has now been found that dialkylation (to be defined below) at the 1'-aminoethyl position of a 3-pyrrolidine substituent removes one asymmetric center and results in a group having only one asymmetric carbon atom and thus only two possible optical isomers instead of four isomers. ##STR3##
It has also been found that the removal of one asymmetric center greatly simplifies the synthesis, separation, and purification relative to pyrrolidine in B and C with two asymmetric centers. It has further been found that the R-(1,1-dialkylated-1-aminomethyl)pyrrolidine, when coupled at the 7-portion of a quinolone or naphthyridone leads to antibacterial agents with improved activity and safety, especially as to cytotoxicity.